1. Field of the Invention
The present invention relates to a magnetic recording head having a function of inducing magnetization reversal by applying a microwave magnetic field to a magnetic recording medium and relates to a magnetic read/write apparatus using the magnetic recording head.
2. Description of the Related Art
Recently, a recording density on magnetic read/write apparatuses such as HDDs (Hard Disk Drives) is requested to increase as fast as 40% per year. The surface recording density is expected to become one Tbit/in2 by the year 2012. Improvement of the surface recording density requires miniaturizing magnetic write and read heads and reducing particle sizes for magnetic recording media. However, miniaturizing a magnetic write head decreases the recording magnetic field strength. This may cause insufficient recording capability. Reducing particle sizes for magnetic recording media makes the thermal fluctuation apparent. The particle size reduction also requires increasing the coercive force and the anisotropic energy. As a result, recording becomes difficult. Improvement of the recording capability is the key to improvement of the surface recording density. To address this problem, the assisted recording is proposed. The assisted recording applies heat or a microwave magnetic field to temporarily decrease the coercive force of a magnetic recording medium only during recording. For example, Patent Document 1 describes an assisted recording technique that applies heat.
An assisted recording technique of applying a microwave magnetic field is termed “microwave assisted magnetic recording” (MAMR) and receives much attention recently. MAMR applies a microwave magnetic field to a nanometer region and locally excites the recording medium to record information while reducing magnetization reversal magnetic fields. Since the magnetic resonance is used, greatly reducing a magnetization reversal magnetic field requires using a strong microwave magnetic field having a frequency that is proportional to the anisotropy field of recording media. Patent document 2 discloses a microwave oscillator that generates a microwave-assisted magnetic field and is structured to sandwich a laminated film structured similarly to a GMR device (Giant Magneto Resistive device) between electrodes. The microwave oscillator can generate a tiny microwave oscillation magnetic field. To do this, the microwave oscillator injects a conduction electron having spin fluctuation generated in the GMR structure into a magnetic material via a nonmagnetic material. Non-patent document 1 reports the microwave oscillation based on spin torque. Non-patent document 2 describes “Microwave Assisted Magnetic Recording.” According to the technology, a microwave magnetic field generation layer or a Field Generation Layer (FGL) fast rotates based on spin torque and is provided near a magnetic recording medium adjacent to the main magnetic pole of a vertical magnetic head. The layer generates microwave (microwave magnetic field) to record information on a magnetic recording medium having large magnetic anisotropy. Non-patent document 3 discloses the technology that efficiently assists magnetization reversal on magnetic recording media. For this purpose, an oscillator is provided between the main magnetic pole of a magnetic recording head and a shield at the rear of the main magnetic pole. The rotation of a microwave magnetic field is varied in accordance with the recording magnetic field polarity. The shield is widely used for magnetic heads as current products in order to improve the recording magnetic field gradient along a head travel direction. For MAMR, the shield is used to change the rotation direction of the microwave magnetic field for an oscillator in accordance with the recording magnetic field polarity. The magnetization efficiently reverses when the microwave magnetic field of the oscillator rotates in the same direction as the precession movement of magnetization on a magnetic recording medium to be reversely magnetized. This technology can assist the magnetization reversal using the microwave magnetic field that always ensures an efficient rotation direction.